Ill-advised. Your father is in more trouble than he was if he now says the statement he made to police was not true. All but the unlawful taking present no problem to them to the prosecution, whatever he says, since they all appear to be matters of police evidence. As said, it's the prosecution who decide whether to proceed with a prosecution. They may proceeed with the taking a conveyance ("theft") charge anyway, even to the extent, if your father has made a formal, signed, statement of evidence, of compelling him to attend the trial and calling him as a witness. In such circumstances he'd be brave if he then told the court that what he'd said in his witness statement was lies !
At best, in retracting what he said , he's been wasting police time and, as said, if he now says he knew of the driving and consented, he risks being prosecuted for assisting in that offence of disqualified driving and permitting driving with no insurance. That's far more trouble than saying the taking was without his consent !
His best answer is to speak or write on the defendant's behalf, providing her with mitigation. He should speak to her solicitor about that.